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Navegando por Assunto "Sm-Nd em rocha total"

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    Evolução da porção Nordeste do Domínio Bacajá a partir de dados U-Pb e Lu-Hf em zircão e Sm-Nd em rocha total
    (Universidade Federal do Pará, 2019-12-29) MAGALHÃES, Lucas Baía; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
    The north-northeast border of the Amazonian Craton is defined as an extensive paleoproterozoic belt whose evolution is related to the Transamazonic Cycle (2.2 - 1.95 Ga). In the southern segment of this belt, in the Central Brazil Shield, is located the Bacajá Domain that consists of portions formed in the Archean and Rhyacian orogens. This Domain is composed of intrusive granitoids and charnockitoides, orthognaisses, granulites, migmatites and supracrustal rocks. In this study, by petrographic analysis, geochronological data U-Pb and Lu-Hf in zircon and Sm-Nd in total rock, it was possible to elaborate an evolution of the continental crust of this region from the Neoarchean to the Rhyacian, highlighting the relationship of the Archean terranes with the granitoids/charnockitoides correlated to the Transamazonic Cycle. Orthognaisses located to the north of Tucuruí Sheet (Aruanã Complex) present strong features of retrometamorphism identified in typical high metamorphic textures (granoblastic/interlobed textures) by association with a lower grade hydrated mineral amphibole assembly (Anf) and biotite (Bt). Coronitic textures and orthopyroxene (Opx) pseudomorphs for Anf and Bt and the presence of antipertites are also evidences that corroborate this phenomenon. These orthognaisses are 2630 ± 15 Ma, the oldest record obtained in this study. They represent fragments of a reworked crust (ɛHf(t) have subchondritic values of -0.3 to -1.7 and ɛNd(t) = - 3.08 to -2.98) whose model ages Hf-TDM C and Nd-TDM indicate that the material giving rise to this orthognaisses was extracted from the mantle in the Mesoarchean (3.0-3.2 Ga). The Rhyacian intrusive suites are characterized by an association of massive granitoids and charnockitoids with well-defined hypidiomorphic granular texture and rocks deformed by the effects of shear zones. In this area is also described a xenolith of orthogranulite characterized by polygonal granoblastic texture. These rocks were placed in the period of 2.12-2.09 Ga and 2.08-2.06 Ga and crystals of the orthogranulite identify a high-grade metamorphic event ca. 2.09 Ga. The identified zircons of the 2.12 Ga orthogranulite are interpreted as related to a magmatic arc (pre-collisional stage) on the edge of a Neoarchean continent. In addition, the isotopes of Pb and Hf show that the 2.12 Ga rock formed from an accreted neoarcan crust (ca. 2.6 Ga), which suffered a high grade 2.09 Ga metamorphic event (in a decompression stage). Finally, the igneous rocks from 2.08 to 2.06 NE of the Bacajá domain formed from the continental crust accreted during the Neoarchean (2.8-2.5 Ga) and that the post-collisional magmatic event of DB extended to 2.06 Ga.
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    Petrografia, geoquímica e geocronologia de rochas vulcano- plutônicas orosirianas do SE do Cráton Amazônico: um estudo da fronteira dos domínios Tapajós e Iriri-Xingu
    (Universidade Federal do Pará, 2020-06-16) SILVA, Amanda Suany Marinho da; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136
    The central part of the Amazonian Craton encompasses the Tapajós (TJD) and Iriri-Xingu (IXD) tectonic domains, which record volcano-plutonic events from the Orosirian times. The boundary between both domains was proposed from Nd isotopes and is marked by the predominance of juvenile paleoproterozoic sources or with little participation of the archaean crust for the TJD, whereas the rocks of the IXD present archaean crustal sources. However, the boundary between these domains is still subject of discussion due to the lack of isotopic data, the homogeneity of the lithotypes and the absence of tectonic structures that could outline this frontier. The study area is in the municipality of Trairão, southwestern Pará state, the probable boundary region between TJD and IXD, where there are occurrences of paleoproterozoic volcano-plutonic associations. We performed in situ U-Pb on zircon by plasmainduced mass spectrometry with laser ablation (LA-ICP-MS), Sm-Nd whole-rock by thermal ionization mass spectrometry (TIMS), together with geochemical analyses and petrographic data aiming to reconstruct the tectonic and chronological emplacement of the magmatic rocks, as well as to better establish the boundary between TJD and IXD. In the study area, the volcanic sequences are represented by the Moraes Almeida, Salustiano and Aruri formations, and the plutonic units correspond to the Creporizão, Parauari (granodioritic and granitic units) and Maloquinha suites. The effusive and volcanoclastic rocks are rhyolites, dacites, andesites, rhyolitic ignimbrites, and tufts. The plutonic units are granodiorites, quartz monzonites, monzogranites, and syenogranites. The geochemical results showed that the rocks of the Creporizão and Parauari intrusive suites (granodioritic and granitic units) have high-K calcalkaline to shoshonitic signature, a meta to peraluminous character, with enrichment in LILE (K, Rb, Ba, and Sr), moderate fractionation of heavy ETR and weak negative Eu* anomalies. Distinctively, the granitoids of the Maloquinha Intrusive Suite and the Salustiano and Moraes Almeida formations have a high-K calc-alkaline signature, from peraluminous to peralkaline character. These rocks present enrichment in HFSE (Zr, Hf, and Th), high ETR contents and pronounced negative Eu* anomalies. In tectonic environment classification diagrams, the granitoids of the Creporizão and Parauari (granitic and granodioritic units) intrusive suites and, Salustiano and Aruri formations showed geochemical affinities with volcanic arc granites (VAG), related to magmatic arc, while the rocks of the Maloquinha Intrusive Suite and the Moraes Almeida Formation are related to intraplate anarogenic environment. The U-Pb zircon dating allowed to identify the oldest plutonic and volcanic rocks, belonging, respectively, to the Intrusive Creporizão Suite, with crystallization age of 1980±6 Ma, and to the unit mapped xi as Salustiano Formation, aged of 1975±11 Ma. The rocks of the Maloquinha Intrusive Suite were generated at 1880±9 Ma, with a volcanic correspondent of the Moraes Almeida Formation of 1877±14 Ma, followed by the plutonic rocks of the Parauari Intrusive Suite (granodioritic unit, aged of 1876±9 Ma, and the granitic unit, of 1867±15 Ma), and the volcanic rocks of the Aruri Formation, generated at 1867±7 Ma. The geochemical characteristics combined with the geochronological data allowed to define a geodynamic evolution involving an context related to magmatic arc environment at ca. 1.98 Ga, which favored the formation of the rocks of the Intrusive Suite Creporizão and Salustiano Formation, followed by an intraplate extensional environment (ca. 1.88 Ga), marked by the coexistence of the types A and I rocks of the Maloquinha and Parauari (granodioritic and granitic units) suites, and Moraes Almeida and Aruri formations. Model ages Nd-TDM (2.31-2.64 Ga), with slightly to strongly negative values of εNd(t) (-1.39 to -7.11), indicate magmas derived from the melting of crustal sources of the Paleoproterozoic and Archaean. These results allowed to draw an NW-SE line, where mainly rocks of paleoproterozoic (<2.5 Ga) and archaean (> 2.5 Ga) model outcrop, belonging, respectively, to the TJD and IXD.
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